Acid Rain  Environmental Effects of Acid Rain Acid rain, more accurately termed acid deposition, has been studied for many years. Numerous environmental effects have been attributed to acid deposition. Perhaps one of the best-known is acidification, a condition in which lakes and streams have a low pH level, resulting in the death of fish and other animal and plant life. Acidification can be chronic, where a given surface water body has a constantly low pH value, or episodic, where pH levels decrease for brief periods due to runoff from melting snow or heavy rain. U.S. areas prone to chronic acidification include the Adirondacks and Catskill Mountains in New York State, the Appalachians, the upper Midwest, and mountainous areas in the western U.S. One of the most acidic lakes in the U.S. is Little Echo Pond in Franklin, New York, with a pH of 4.2. In the New Jersey Pine Barrens, over 90% of streams are acidic. Episodic acidification, which can be severe enough to cause fish kills, is common in the mid-Appalachian region, where it affects approximately 30% of sensitive streams, and in the Adirondacks, where 70% of sensitive lakes are at risk. In eastern Canada, 14,000 lakes are extremely vulnerable to chronic acidification. Acidification also occurs in much of Scandinavia and in parts of the United Kingdom and the Alps. Forest damage is another environmental effect related to acid deposition. A 1999 survey of European forests showed that one out of every four trees had suffered the loss of 25% or more leaves or needles. Tree damage is believed to have multiple causes, including acidification of soil and high concentrations of ground-level ozone, both side-effects of acidic deposition. In Germany, this phenomenon, first observed in the Black Forest in the 1960s, is termed Waldsterben or tree death. An example is shown in the photo above. Damage was first observed in conifers, then later in deciduous trees, such as oak and beech. By 1990, nearly half the trees in the Black Forest were damaged. Soils are also affected by acid deposition, particularly in areas with highly siliceous bedrock (granite, gneisses, quartzite, and quartz sandstone). These soils, which are common in eastern North America and Scandinavia, are already somewhat acidic. When acid deposition occurs on acidic soils, important cations including potassium, calcium, magnesium, and sodium are readily leached out, making them unavailable to plants as nutrients. This phenomenon, termed soil depletion, reduces the fertility of the soil. Similarly, in areas with old, highly leached soils, acid deposition depletes the small amounts of cations present, and the soil soon becomes unable to support plant life. In contrast, soils rich in calcium, potassium, magnesium, and sodium are more resistant to the effects of acid deposition. These soils, common in arid and semi-arid regions such as the Utah desert shown above, are naturally alkaline and have the ability to buffer acid deposition. Much of the western U.S. is at less risk for acid deposition for this reason. The buffering capacity of alkaline soils can, however, be depleted by continuous acid deposition. Many plants and animals are sensitive to acidification. The vulnerability of fish and other small aquatic organisms is well-established. As acid precipitation flows through soils, aluminum is released. As pH in a lake or stream decreases, aluminum concentration increases. Both low pH and high aluminum concentrations are toxic to fish. Frogs are relatively tolerant of low pH, but the insects upon which they feed are not. Lichens, mosses, and fungi are also particularly sensitive to acid deposition. Human health is indirectly affected by acid deposition through the consumption of toxic metals that entered the food chain during soil acidification. Other environmental problems are closely related to acid deposition. Eutrophication is a term used to describe aging of a lake or shallow marine areas such as coastal zones. The aging process can be natural, resulting from the accumulation of nutrients, sediments, silt, and organic matter in from the surrounding watershed. Eutrophication can also be caused by human activity. This is called cultural eutrophication and is associated with excess nitrogen and, to a lesser extent, excess phosphorous, from agricultural activities, sewage, and industrial waste. Algal blooms, such as the red tide event in coastal Hong Kong illustrated above, are a symptom of eutrophication. If eutrophication is ongoing, a decline in biodiversity may result. Ground-level ozone is formed in the atmosphere by nitrogen oxides and volatile organic compounds in the presence of sunlight. Ground-level ozone causes damage to agricultural crops and trees, and is harmful to human health. Ground-level ozone commonly reaches harmful concentrations in cities around the world. It is particularly problematic in urban areas with heavy motor vehicle traffic combined with a tendency to trap local air pollution, such as through temperature inversions or by nearby mountain ranges. Acid deposition is well-known for its corrosive effects on buildings and monuments made of sensitive materials such as limestone or sandstone. An example is shown at left. These easily weathered materials are slightly soluble in normal rainwater. In the presence of acid deposition, weathering rates are greatly increased. EPIC FIGHT EVER